Integrated optical control element and a method for fabricating the same and optical integrated circuit element and optical integrated circuit device using the same

Abstract

The integrated optical control element of this invention includes: a first waveguide for allowing light incident from outside to propagate therein; a multilayer structure for allowing the light which has propagated in the first waveguide to be incident thereon and for transmitting the light therethrough or reflecting the light therefrom, the multilayer structure including at least one layer having a refractive index different from an equivalent refractive index of a region with which the at least one layer is in contact; and a second waveguide for receiving at least part of the light transmitted through or reflected from the multilayer structure.

What is claimed is: 
     
       1. An integrated optical control element comprising: a first waveguide for allowing light incident from outside to propagate therein;   a multilayer structure for allowing the light which has propagated in the first waveguide to be incident thereon and for transmitting the light therethrough or reflecting the light therefrom, the multilayer structure including at least one layer having a refractive index different from an equivalent refractive index of a region with which the at least one layer is in contact; and   a second waveguide for receiving at least part of the light transmitted through or reflected from the multilayer structure,   wherein each of the first waveguide and the second waveguide is a channel type waveguide in which a propagating light is confined in a lateral direction of the waveguide.   
     
     
       2. An integrated optical control element comprising: a first waveguide for allowing light incident from outside to propagate therein;   a multilayer structure for allowing the light which has propagated in the first waveguide to be incident thereon and for transmitting the light therethrough or reflecting the light therefrom, the multilayer structure including at least one layer having a refractive index different from an equivalent refractive index of a region with which the at least one layer is in contact; and   a second waveguide for receiving at least part of the light transmitted through or reflected from the multilayer structure,   wherein the multilayer structure includes two or more layers having different refractive indexes, each of the two or more layers have a thickness expressed by:   (2m+1)λ.sub.0 /(4n cos θ)     where λ 0  is a wavelength of light in a vacuum, θ is an angle formed by a light proceeding direction and a normal of a layer, n is a refractive index thereof, and m is an integer more than 0.     
     
     
       3. An integrated optical control element according to claim 2, wherein the mode of the light incident on the multilayer structure from the first waveguide is a TM mode, and the angle θ is 45° or more. 
     
     
       4. An integrated optical control element comprising: a first waveguide for allowing light incident from outside to propagate therein;   a multilayer structure for allowing the light which has propagated in the first waveguide to be incident thereon and for transmitting the light therethrough or reflecting the light therefrom, the multilayer structure including at least one layer having a refractive index different from an equivalent refractive index of a region with which the at least one layer is in contact; and   a second waveguide for receiving at least part of the light transmitted through or reflected from the multilayer structure,   wherein the first waveguide includes a first core layer which becomes a core for guiding the light, and a first cladding layer located below the first core layer and having a refractive index smaller than that of the first core layer;   the second waveguide includes a second core layer and a second cladding layer located below the second core layer and having a refractive index smaller than that of the second core layer;   the multilayer structure is located below the second cladding layer; and   the thickness of the second cladding layer is set at a value equal to or more than 0.3 times and equal to or less than 2.1 times of a distance where a beam intensity at the first waveguide decreases from a maximum value to a value of exp(-2) times the maximum value in the first cladding layer.   
     
     
       5. An integrated optical control element comprising: a first waveguide for allowing light incident from outside to propagate therein;   a multilayer structure for allowing the light which has propagated in the first waveguide to be incident thereon and for transmitting the light therethrough or reflecting the light therefrom, the multilayer structure including at least one layer having a refractive index different from an equivalent refractive index of a region with which the at least one layer is in contact; and   a second waveguide for receiving at least part of the light transmitted through or reflected from the multilayer structure,   wherein the first waveguide includes a first core layer which becomes a core for guiding the light, and a first cladding layer located below the first core layer and having a refractive index smaller than that of the first core layer,   the second waveguide includes a second core layer and a second cladding layer located below the second core layer and having a refractive index smaller than that of the second core layer,   the multilayer structure is located below the second cladding layer, and   the thickness of the second cladding layer is a value obtained from:   mλ.sub.0 / 2n.sub.2 {1-(n.sub.0 sin θ/n.sub.2).sup.2 }.sup.1/2 !     where λ 0  is a wavelength of light in vacuum, n 0  is a refractive index of the first core layer, n 2  is a refractive index of the second cladding layer, θ is an angle formed by a light propagating direction in the first core layer and a normal of the multilayer structure, and m is an integer more than 0.     
     
     
       6. An optical integrated circuit element comprising a substrate and a plurality of optical elements formed integrally on the substrate, the optical elements including at least one integrated optical control element of claim 1. 
     
     
       7. An optical integrated circuit element according to claim 6, further comprising a multi-function semiconductor laser for supplying light to the at least one integrated optical control element, which outputs a plurality of coherent laser beams. 
     
     
       8. An optical integrated circuit element according to claim 6, wherein the optical integrated circuit element is an optical integrated circuit element for coherent detection and further comprises a laser for local oscillation for supplying light to the at least one integrated light control element. 
     
     
       9. An optical integrated circuit element according to claim 6, wherein the at least one integrated optical control element is a light demultiplexing element for dividing one input beam into a plurality of output beams. 
     
     
       10. An optical integrated circuit element according to claim 8, wherein the optical integrated circuit element further comprises a plurality of waveguides, and the multilayer structure is directly formed on a waveguide end face in the at least one integrated optical control element for guiding signal light input from outside. 
     
     
       11. An integrated optical control element comprising: a waveguide including a first layer as a core for guiding light and second and third layers located above and below the first layer, respectively, each of the second and third layers having refractive indexes smaller than that of the first layer;   a concave portion formed in a portion of the waveguide, the concave portion extending through at least the first layer and either one of the second and third layer which is closer to the substrate, the concave portion dividing the waveguide into a first waveguide portion and a second waveguide portion; and   a multilayer structure formed inside the concave portion by sequentially forming a plurality of layers inside the concave portion,   wherein the waveguide is a channel type waveguide in which the propagating light is confined in a lateral direction of the waveguide.   
     
     
       12. An integrated optical control element comprising: a waveguide including a first layer as a core for guiding light and second and third layers located above and below the first layer, respectively, each of the second and third layers having refractive indexes smaller than that of the first layer;   a concave portion formed in a portion of the waveguide, the concave portion extending through at least the first layer and either one of the second and third layer which is closer to the substrate, the concave portion dividing the waveguide into a first waveguide portion and a second waveguide portion; and   a multilayer structure formed inside the concave portion by sequentially forming a plurality of layers inside the concave portion,   wherein the refractive index of a layer formed finally among the plurality of layers constituting the multilayer structure is larger than a refractive index obtained from n 0  sinθ where n 0  is a refractive index of the first layer and θ is an angle formed by a light propagating direction in the first layer and a normal of the multilayer structure and is smaller than that of the other layer or layers of the multilayer structure.   
     
     
       13. An integrated optical control element comprising: a waveguide including a first layer as a core for guiding light and second and third layers located above and below the first layer, respectively, each of the second and third layers having refractive indexes smaller than that of the first layer;   a concave portion formed in a portion of the waveguide, the concave portion extending through at least the first layer and either one of the second and third layer which is closer to the substrate, the concave portion dividing the waveguide into a first waveguide portion and a second waveguide portion; and   a multilayer structure formed inside the concave portion by sequentially forming a plurality of layers inside the concave portion,   wherein the refractive index of the thickest layer among the plurality of layers constituting the multilayer structure is larger than a refractive index obtained from n 0  sinθ where n 0  is a refractive index of the first layer and θ is an angle formed by a light propagating direction in the first layer and a normal of the multilayer structure and smaller than a refractive index of the other layer or layers of the multilayer structure.   
     
     
       14. An optical integrated circuit device comprising a plurality of optical elements in combination, wherein at least one of the plurality of optical elements is the integrated optical control element of claim 1. 
     
     
       15. An optical integrated circuit device according to claim 14, further including a multi-function laser for supplying light to the integrated optical control element, which outputs a plurality of coherent laser beams. 
     
     
       16. An optical integrated circuit device according to claim 14, wherein the optical integrated circuit device is an optical integrated circuit device for coherent detection and further includes a laser for local oscillation for supplying light to the integrated optical control element. 
     
     
       17. An optical integrated circuit device according to claim 16, wherein the optical integrated circuit device is an optical integrated circuit device for coherent detection where local oscillation light and signal light are input from outside to the integrated optical control element including a plurality of waveguides, and the multilayer structure is directly formed on a waveguide end face in the integrated optical control element for guiding the signal light.